A color image copying process in which beams of light carrying the image information of a color original are applied on a color photo sensitive material so as to expose the material and then the material is developed and fixed by the processing section of a copying machine is known in the art.
In the copying machine of this type, it is required that the color of the light carrying an image information can be corrected according to the spectral-sensitivity characteristic of the color sensitive material, that the hue of the exposed light can be adjusted in correspondence to the color tone of the original and further that the light can be actively adjusted to a desired hue.
In order to control the hue of the exposed light, a method is employed in which three-color correction filters are inserted midway in an optical path for the image carrying light and the amounts of insertion of the correction filters (the ratios of insertion) are controlled.
As such three-color correction filters, those which can shield the wavelength of light of specific hue are used. More concretely, a yellow filter which is capable of shielding blue light, a magenta filter which is capable of shielding green light and a cyan filter which is capable of shielding red light are used. In this case, an exposure control by the two kinds of filters is considered in view of the easiness of control and the loss of the amount of light due to shielding of light by the filter. But since the amount of light varies depending on the amount of insertion of each filter into the optical path, there is often a case in which a complete color adjustment is difficult because loss of light due to the degree of insertion of the filter is not compensated in an appropriate manner.